A floating seal incorporated in a track roller assembly of a construction machine is used for the purpose of preventing penetration of earth and sand. It has therefore good corrosion resistance and often produced from hard, high-carbon, high-Cr cast iron which is improved in seizure resistance and wear resistance by crystallization of a large amount (30% by volume or more) of Cr7C3 carbide having high hardness. The contact surface of a floating seal that is required to slide under a higher speed condition is coated with cemented carbide composed of WC and self-fluxing alloy by thermal spraying.
Wear-resistant contact materials such as thrust washers used for the end faces of work implement bushings, which are required to slide without seizing under a higher surface pressure, lower speed, grease-lubricated condition and to have wear resistance and load resistance as important factors, are usually made from carburized or induction-hardened steel. For reducing greasing frequency to meet the demand for easy maintenance, the following measure is sometimes taken in recent years. Specifically, in the joint of a work implement of a construction machine for example, an oil-bearing bushing formed by impregnating a work implement bushing with lubricating oil is used and a thrust washer is disposed on the end faces of the bushing, which thrust washer is formed from steel that is coated with a seizure-resistant, wear-resistant cemented carbide composed of WC/self-fluxing alloy by thermal spraying.
As a prior art technique associated with the present invention, a method of adding alloy elements to effectively enhance the temper softening resistance of a martensite parent phase has been proposed by us in Japanese Patent Application Nos. 2002-135274 and 2002-240967.
The above-described floating seal for hermetically sealing a track roller assembly to confine lubricating oil has revealed the problem that since fine earth/sand particles creep onto the sealing surface owing to their rubbing motion within the floating seal mechanism while wear is progressing and the sealing surface is lubricated with the confined lubricating oil, the lubricating condition is extremely severe, so that as the setting pressure (i.e., pressing force) under which the floating seal is assembled increases, seizure, quenching cracks and abnormal wear are more likely to occur on the sliding contact surface, which results in oil leakage.
The latest construction machines such as bulldozers are required to have improved work efficiency during high speed traveling, and therefore, the floating seal has to rotate at high speed, which results in seizure, quenching cracks and abnormal wear accompanied with oil leakage as described above.
While there is a demand for a cost reduction by increasing the service life of the track roller assembly and others, the current wear-resistant cast steel materials cannot exert wear resistance good enough to meet the demand.
Further, the thermal-spray-coated thrust washer for use in a bearing part of a work implement suffers from the problem that biting of penetrating earth and sand causes damage to the washer.
Although it has been contemplated that the cold tool steel (SKD material), high speed steel (SKH material) and the like may be applied as a material for improving the seizure resistance and wear resistance of a floating seal and a thrust washer, such tool steels do not necessarily have satisfactory seizure resistance and wear resistance. Moreover, such tool steels are costly and therefore the costs of material and machining work are too high when taking account of the yield of the material consumed to obtain a finished product.
The present invention is directed to overcoming the foregoing problems and a primary object of the invention is therefore to provide a wear-resistant iron-based sintered contact material that is produced by powder sintering so as to have high density, high seizure resistance and wear resistance. Another object of the invention is to provide a low-strain, wear-resistant, iron-based sintered composite contact component and a producing method thereof, the component being formed such that instability in the accuracy of configuration/dimension caused by compaction during a sintering process is avoided by sinter-bonding the material of the above wear-resistant iron-based sintered contact material to a backing metal during a sintering process in the production of the wear-resistant iron-based sintered contact material.